Liquefied petroleum gas, also called LPG, GPL, LP Gas, liquid petroleum gas or simply propane or butane, is a flammable mixture of hydrocarbon gases
used as a fuel for cooking, heating, commercial appliances and vehicles. When specifically used as a vehicle fuel it is often referred to as auto-gas.
LPG is prepared by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil),
or extracted from petroleum or natural gas streams as they emerge from the ground. It was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912.
It currently provides about 3% of all energy consumed, and burns relatively cleanly with no soot and very few sulfur emissions.
As its boiling point is below room temperature, LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurised steel vessels, normally called LPG cylinders.
They are typically filled to between 80% and 85% of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporised gas and the liquefied gas
varies depending on composition, pressure, and temperature, but is typically around 250:1.
Large amounts of LPG can be stored in bulk cylinders and can be buried underground.